I did move it to its seperate stand isolated from the rifle 2-3 feet away and got 905 so kinda in beteeen the other reading.
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Chronograph distance
- Thread starter Crabbypatties
- Start date
ok - it could be down to the Chronographs resolution & is actually giving "valid" results.
If you cant sleep - watch my 40min tear down vid of another barrel mounted chrony, specifically this part: You can see that it cant tell the difference between 995 & 1000fps as it doesnt have the resolution.
This is actually not too bad for a chrony & there's a good chance that yours is worse.
So what you could be seeing is that at those distances - is the pellet is slowing down & jumping into each of those "speed brackets" as it decelerates.
If you did a heap of shots, you'll most likely find a heap of results at exactly 2 different speeds, i.e. 895.12... 895.12... 898.75... 895.12.... 898.75
Which is the pellet around the boundary of a speed bracket.
If you cant sleep - watch my 40min tear down vid of another barrel mounted chrony, specifically this part:
This is actually not too bad for a chrony & there's a good chance that yours is worse.
So what you could be seeing is that at those distances - is the pellet is slowing down & jumping into each of those "speed brackets" as it decelerates.
If you did a heap of shots, you'll most likely find a heap of results at exactly 2 different speeds, i.e. 895.12... 895.12... 898.75... 895.12.... 898.75
Which is the pellet around the boundary of a speed bracket.
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Interesting. I figured there is obviously a resolution limit which I guess was 2–3%. But how does that explain shooting 890 and then removing action from stock and shooting 920 on next shot. That’s not within resolution or binning error.
I later checked elevation as with just action it was shooting low over the chrony so I raised the action and still around 920. Think it was 916. So that eliminated elevation.
Only change was muzzle distance to chrony.
But I agree with your video. If resolution is only 2-4 FPS the decimal output is just there to make you think it’s more accurate then it actually is.
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Quick reminder - 2% of 1,000fps = 20fps
so a few percent is a HUGE amount when it comes to Chrony's working @ 1,000fps
hmnmm Is the rifle fixed?
If the stock is adding weight - removing it could be causing it to jump back a little & taking a bit out of the projectile.
Is the chrony isolated from the table the rifle is on? Could the movement of the rifle be transferring movement/vibrations to the Chrony?
so a few percent is a HUGE amount when it comes to Chrony's working @ 1,000fps
hmnmm Is the rifle fixed?
If the stock is adding weight - removing it could be causing it to jump back a little & taking a bit out of the projectile.
Is the chrony isolated from the table the rifle is on? Could the movement of the rifle be transferring movement/vibrations to the Chrony?
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I don’t know what type of pcp you have but some suffer from not having a proper vent in the stock for the hammer. When the receiver is in the stock, the air in front of the hammer cannot escape quick enough and slows the hammer’s velocity, causing a lower velocity shot.
Just something to check.
Dave
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Interesting.. Never considered that.
This particular rifle is the Reximex Daystar in a solid Walnut Stock. So no vents for sure anywhere on the stock.
Mike
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Good catch the 2% at 1000, but in my mind I was thinking 2-3 FPS not %. Brad Fart in typing.
The rifle out of stock is sitting on a bag and the rear is supported by a 2x4 so it's resting on the bench. The crony is on the bench so not isolated.
When rifle is in stock its sitting on bi-pod and I am holding rear, so I guess more isolated from the bench.
MIke
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2-3fps @ 1,000 is pretty good - not a huge amount of Chronys will be offering that.
Make the distance the same in/out of the stock for starters, then possibly isolate the chrony - put it on another bench & fix it to something heavy is possible.
While it may sound silly (my job is to test Chony's back to back with calibrated units - and i've done hundreds & hundreds) - vibrations can really *really* matter...
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I use the FX 2 pocket chrono, I have no idea what distance its measuring speed from but seems to work good enough for me. I have mounted it on the side pic rail and the muzzle/moderator (probably about a foot difference) with the same results.
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The FX is a radar unit I believe so its slightly different then the optical ones that use light sensors.
Mike
Mike
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